Formulators of fibrous structures have conventionally been faced with a contradiction. Formulators have desired to increase tensile breaking strength of fibrous structures, however, doing so also brings about the effect of negatively increasing the drainage properties (as measured by pfr) of the fibrous structure. In through-air-dried processes for making fibrous structures, the incremental increase in tensile breaking strength has not been worth the negative increase in drainage properties due to the amount of energy needed to remove the additional water during the wet-laid fibrous structure making process. These negatives are not present during a wet-pressing fibrous structure making process.
Accordingly, there is a need, especially for through-air-dried fibrous structures, to increase tensile breaking strength without negatively increasing the drainage properties of the fibers and/or fibrous structure containing such fibers. In addition, there is a need for a process for making such fibrous structures, for treating fibers used in such fibrous structures, and for making sanitary tissue products comprising such fibrous structures.